Optical glass fibers typically include a waveguide formed by a central core surrounded by a cladding material. The core and cladding are usually coated with at least one additional layer to help protect the delicate waveguide during handling and to shield the waveguide against external stresses that may cause microbend losses, etc. A common configuration is to directly coat the cladding with a relatively soft “primary” coating, and then apply a harder “secondary” coating onto the primary coating. Coloration to identify the fiber may be applied, either by incorporating colorants in the secondary coating or applying a very thin coating of an ink over the secondary coating.
In some cases, an additional protective outer coating referred to as a buffer jacket material is applied over the secondary coating. In certain situations, the buffer jacket material is made of a thermoplastic material, for example polyvinyl chloride (PVC), polyethylene, or nylon. In some situations, the buffer jacket material is made of an ultra-violet (UV) curable polyacrylate. The buffer jacket outer layer can be configured to provide desired mechanical protection to the core and cladding. For example, conventional buffer jacket outer layers may be relatively soft to help cushion the core and cladding from external stresses or relatively harder to help protect the core and cladding layer and to effectively shield the optical fiber from certain external forces and stresses. This buffer coating may also improve the ergonomics of handling the relatively delicate optical fiber in the field by providing a larger, more robust structure for installers to handle.
The protective buffer jacket outer layer may be applied on the coated optical fiber to create a “semi-tight buffer optical fiber” or a “tight-buffer optical fiber.” While the buffer jacket outer layer provides protection to the optical fiber, at least a portion of the buffer jacket outer layer must be removed in order to terminate the optical fiber and put it in use. One such method is to remove a small section of the tight buffer to terminate the optical fiber in an optical connector. Another method is to remove long lengths of the tight buffer in order to terminate the fiber by fusion splicing. In many situations, an installer of optical fiber may need to remove all of the buffer jacket outer layer for up to one linear meter of the optical fiber in order to properly terminate the optical fiber, while leaving the primary and secondary coating layer on the optical fiber. Removing up to one linear meter of the buffer jacket outer layer can be difficult because conventional buffer jacket outer layers are not designed to be peeled off the coating layer of the coated optical fiber. This means the installer will have to slide the buffer jacket outer layer off of the coating layers of the coated optical fiber. This can be difficult if the buffer jacket outer layer does not slide easily along the coating layer of the coated optical fiber.
In order to improve the ability for an installer to remove the buffer jacket outer layer from the coated optical fiber, one form of tight-buffer optical fiber may include a substantial void filled with an additional material between the coated optical fiber and the buffer jacket outer layer. FIG. 1 presents one common version of a conventional tight-buffered optical fiber 100. As shown in FIG. 1, the tight-buffered optical fiber 100 can include an optical fiber having a central core 102. The central core 102 can be surrounded by cladding material 103 that has a generally circular cross-section. The conventional tight-buffered optical fiber can also include one or more of a primary coating layer 104 surrounding the cladding material 103, a secondary coating layer 106 surrounding the primary coating layer 104 and a tertiary coating layer (not shown) surrounding the secondary coating layer 106, which may be collectively referred to herein as a “coating layer 106”. The central core 102, the cladding material 103, and the coating layer 106 make up the optical fiber. In certain examples, the primary coating layer 104 can be relatively soft while the secondary coating layer can be relatively hard. The coating layer may be colored or colorless. For example, in conventional embodiments where the coating layer includes a primary coating layer 104 and a secondary coating layer 106, the secondary coating layer may be colored. In other conventional embodiments, the primary coating layer 104 and the secondary coating layer 106 are colorless and the tertiary layer is a thin ink layer covering the secondary coating and providing a color thereto. A slip layer 108 can be applied around an exterior of the coating layer 106 (e.g., the secondary coating layer 106 or ink layer). The slip layer 108 can act as a lubricant between the coating layer 106 and the inner surface of the buffer jacket outer layer 110 (e.g., between the secondary coating layer 106 or ink layer (if applied) and the buffer jacket outer layer 110). The slip layer 108 can be an oil-based filling compound or gel. Examples of the materials used for the slip layer 108 include lubricants, such as silicone oil, thixotropic materials and acrylate material.
However, the use of slip layers 108 to provide an improved mechanism for removing the buffer jacket outer layer 110 from at least a portion of the optical fiber 100 can have several drawbacks. First, to apply the slip layer 108 requires an additional step in the manufacturing process for the optical fiber 100. This additional step is needed in order to apply the slip layer 108 to the outer surface of the coating layer 106 (e.g., the secondary coating layer 106 or ink layer). The additional manufacturing step results in additional costs and additional time to manufacture the tight-buffered optical fiber 100. In addition, once a user removes the buffer jacket outer layer 110 from the optical fiber 100, the user must then attempt to clean off the oil, gel, or other wet filling compound that remains on the outer surface of the coating layer 106 (e.g., the secondary coating layer 106 or ink layer) before the user can terminate the optical fiber 100 for use. This cleaning process can be time-consuming and, in many cases, it can be very difficult to remove a sufficient amount of the slip layer material 108 from the outer surface of the coating layer 106 (e.g., the secondary coating layer 106 or ink layer).
Another example of conventional tight-buffered optical fibers includes an optical fiber having a central core 102 and cladding material 103 surrounding an outer surface of the central core 102. The optical fiber may also include one or more of a primary coating layer 104 surrounding the cladding material 103, a secondary coating layer 106 surrounding the primary coating layer 104 and an optional tertiary coating layer (not shown) surrounding the secondary coating layer 106 (collectively the “coating layer 106”), The outer surface of the coating layer 106 may then be surrounded by a buffer jacket outer layer that is made from a thermoset acrylate prepolymer generally cured using ultraviolet (UV) radiation. If it is desirable to easily remove long lengths of an acrylate buffer jacket outer layer, additives may be incorporated into the formulation of the buffer jacket outer layer prepolymer to increase the slip capability of the cured buffer jacket outer layer against the coated fiber surface (e.g., the outer surface of the secondary coating layer 106). Unfortunately, this conventional design of an easily removable buffer outer layer also has drawbacks. The use of such slip additives in the buffer jacket outer layer can cause the optical fiber to experience high optical attenuations. High optical attenuations in the optical fiber are not desirable and can occur most frequently during cold weather. The coefficient of thermal expansion of the cured acrylate buffer jacket coating is generally significantly higher than that of the secondary-coated optical fiber. When no slip additive is used, the optical fiber is well-coupled to the buffer jacket outer coating and forms a composite where the buffer jacket outer coating cannot shrink relative to the fiber. However, when a slip additive is used, the buffer jacket outer coating can shrink relative to the secondary coated optical fiber, forcing the fiber to bend and resulting in signal attenuation.
In order to overcome some of the issues of conventional tight-buffered optical fibers, some manufacturers have developed semi-tight buffered optical fibers. FIG. 2 presents one common version of a conventional semi-tight buffered optical fiber 200. As shown in FIG. 2, the semi-tight buffered optical fiber 200 includes an optical fiber having a central core 102. The central core 102 is surrounded by cladding material 103, which has a generally circular cross-section just as that described with regard to the tight-buffered optical fiber of FIG. 1. The conventional tight-buffered optical fiber can also include one or more of a primary coating layer 104 surrounding the cladding material 103, a secondary coating layer 106 surrounding the primary coating layer 104 and a tertiary coating layer (not shown) surrounding the secondary coating layer 106, which may be collectively referred to herein as a “coating layer 106”. In certain examples, the primary coating layer 104 can be relatively soft while the secondary coating layer can be relatively hard. The coating layer may be colored or colorless. For example, in conventional embodiments where the coating layer includes a primary coating layer 104 and a secondary coating layer 106, the secondary coating layer may be colored. In other conventional embodiments, the primary coating layer 104 and the secondary coating layer 106 are colorless and the tertiary layer is a thin ink layer covering the secondary coating and providing a color thereto. The coating layer 106, core 102, and cladding layer 103 are collectively referred to herein as a “coated optical fiber”. An air gap 202 can be provided for around an exterior of the coated optical fiber (e.g., around the exterior of the secondary coating layer 106) between the outer surface of the coating layer 106 (e.g., the outer surface of the secondary coating layer 106 or ink layer) and the inner surface of the buffer jacket outer layer 110. The air gap 202 can provide sufficient spacing to permit the buffer jacket outer layer 110 to slide along the outer surface of the coating layer 106 of the coated optical fiber and be removed from the coated optical fiber 200.
However, the use of an air gap 202 to provide an improved mechanism for removing the buffer jacket outer layer 110 from at least a portion of the optical fiber 200 also has drawbacks. For example, the ability of the coated optical fiber 102, 103, 104, 106 to move around inside of the buffer jacket outer layer 110 can result in the coated optical fiber experiencing high optical attenuations. These high optical attenuations can be most significant when the coated optical fiber is used in an area of cold weather due to the shrinkage of the buffer jacket outer layer relative to the secondary coating layer 106. In addition, the manufacturing process for semi-tight buffered optical fibers 200 can be more challenging as it can be difficult to maintain a constant or substantially constant air gap spacing between the outer surface of the coated optical fiber (e.g., the outer surface of the secondary coating layer 106 or ink layer) and an inner surface of the buffer jacket outer layer 110.